A widely known type of optical sensor is a photointerrupter that comprises a light-emitting device and a light-receiving device for receiving the light from said light-emitting device and which checks for the presence of a light-shielding object between the two devices by determining whether the light generated from the light-emitting device is interrupted by the object.
A conventional type of inclination detecting sensor that adopts a photointerrupter is shown schematically in FIG. 11 and comprises the following components: photointerrupter 71 consisting of a light-emitting device 71a and a light-receiving device 71b that is provided in a face-to-face relationship with the device 71b in such a way as to be capable of receiving the light issuing from it; a resin-molded lower case 72 with the top 72a being open to accommodate the photointerrupter 71; an upper case 73 fitted on the top 72a of the lower case 72; and a light-shielding sector 74 adapted to swing between the light-emitting and receiving devices 71a and 71b about a shaft 73b that is supported on a shaft bearing 73a directed downward from the upper case 73 to extend into the lower case 72.
In this type of optical sensor, the light shield 74 supported on the bearing 73a of the shaft 73b is subject to the gravitational effect and normally positioned below the shaft 73b. For its operation, the sensor is either carried or fixed on an object which to be is checked for the occurrence of inclination greater than a certain angle. If the object and, hence, the sensor is either in a level position or inclined at an angle not exceeding a specified value, the light issuing from the light-emitting device 71a toward the light-receiving device 71b has its optical path blocked by the light shield 74 and is not picked up by the light-receiving device 71b. On the other hand, if the object is inclined in either direction to exceed the specified angle, the light shield 74 is accordingly displaced in position relative to the photointerrupter 71 fixed to the lower case 72 and the light issuing from the device 71a travels uninterrupted by the shield 74 and it is picked up by the light-receiving device 71b, whereupon an electric current flows between the associated lead terminals to enable the detection of the inclination of the object.
With the recent advances in the technologies of semiconductors and optical devices, the demand for optical sensors of the above-described type that employ a photointerrupter has increased, requiring not only a further reduction in the number of parts to be assembled but also the adoption of a simplified fabrication process.
In fact, however, the conventional optical sensors requires that the upper case 73 be equipped with the bearing 73a for enabling the provision of the light shield 74. What is more, the light shield 74 which has a specific form adapted for the detection of inclination must either be provided integrally with the shaft 73b or made as a separate member and thereafter connected to the latter in the assembling step. This increases the complexity of mechanical design, making it difficult to reduce the number of parts below a certain level. It is also difficult to simplify the fabrication process beyond a certain level.